Skip setting owner refs for objects that don't support it

[tomasaschan]

What this PR does / why we need it:

Before this fix, a declarative controller using declarative.WithOwner(declarative.SourceAsOwner) will end up in an infinite reconciliation loop if any of the manifests in the package do not support having the declarative object as its owner.

For example, consider a namespaced declarative object foo/foo of type Foo, installing a package that adds a few objects (say, two Bars) in the same namespace plus another object (say, a Baz) in a fixed namespace qux. With the old behavior of this reconciler, the following happens:

1. The reconciler creates all objects in the package, setting owner references to an object with the same group, version, kind and name as the declarative object, and the same namespace as each respective object from the package. In other words, we get two Bars in foo owned by foo/foo, and a Baz in qux owned by qux/foo.

2. Since qux/foo does not exist, the API server decides that it must have been deleted, and that means qux/baz should also be deleted (its owner no longer exists).

3. The reconciler is notified, and determines that qux/baz is missing, re-adding it again with an owner reference to qux/foo.

4. Go back to step 2.

With the change in this PR, the reconciler will instead skip setting an owner reference on qux/foo, avoiding the infinite loop at the cost of qux/foo now being a "dangling" object; if/when the declarative object foo/foo is deleted, qux/foo will be left untouched in the cluster.

Which issue(s) this PR fixes: Fixes #176

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[rajansandeep]

/ok-to-test

[justinsb]

/approve /lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justinsb, tomasaschan

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